1. Field of the Invention
The present invention relates generally to the field of oxygen scavenging compositions. More particularly, it concerns oxygen scavenging compositions comprising tetrahydrofurfuryl acrylate or vinyl tetrahydrofurfurylate monomers.
2. Description of Related Art
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf-life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking. In the food packaging industry, several means for limiting oxygen exposure have already been developed, including modified atmosphere packaging (MAP), vacuum packaging and oxygen barrier film packaging. In the first two instances, reduced oxygen environments are employed in the packaging, while in the latter instance, oxygen is physically prevented from entering the packaging environment.
Another, more recent, technique for limiting oxygen exposure involves incorporating an oxygen scavenger into the packaging structure. One important class of oxygen scavengers is oxygen scavenging polymers. However, it has been found that some oxygen scavenging polymers, such as polybutadiene and similar polymers, generate fragments upon reaction with oxygen, and the fragments may enter the packaged product and impart an off-taste or malodor.
Ching et al., U.S. Pat. No. 5,627,239, discloses polymers comprising an ethylenic or polyethylenic backbone and hydrocarbyl moieties which contain ether and which are pendant or terminal to the backbone. These polymers, such as ethylene/methyl acrylate/tetrahydrofurfuryl acrylate terpolymer (EMTF), were prepared by reactive extrusion, which led to a crystalline product that underwent significant degradation during the reactive extrusion process.
For packaging oxygen-sensitive food products, it is desirable to eliminate oxygen in the package as soon as possible after the package is sealed. This requires the oxygen scavenger to scavenge oxygen at the highest possible rate and capacity upon initiation of scavenging. The EMTF random copolymer made by reactive extrusion, however, was only capable of scavenging less than 5 cc oxygen per gram of oxygen scavenging polymer in the first day, and about 100 cc oxygen per gram of oxygen scavenging polymer in the second day.
Therefore, it is desirable to have oxygen scavenging polymers that consume oxygen with the highest rate and capacity within the first few days after packaging and initiation in order to most effectively prevent the degradation of product associated with free oxygen in the package. In addition, the incorporation of an oxygen scavenging moiety into a polymer system through reactive extrusion can lead to degradation of the polymer as a result of the high process temperatures required for reactive extrusion. Reactive extrusion also is limited in that the level of incorporation of the oxygen scavenging moiety is determined by the reaction kinetics, and thus, less than 100% of the potential sites for incorporation of the oxygen scavenging moiety.
In one embodiment, the present invention relates to an oxygen scavenging composition, comprising: an oxygen scavenging polymer comprising units having structure I: 
wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls and n is an integer greater than or equal to 1; and,
an oxidation catalyst.
In another embodiment, the present invention relates to a packaging article, comprising:
an oxygen scavenging layer comprising an oxygen scavenging polymer comprising units having structure I, as described above.
In yet another embodiment, the present invention relates to a method of initiating oxygen scavenging by an oxygen scavenging composition, comprising:
(a) providing an oxygen scavenging composition, comprising:
(i) an oxygen scavenging polymer comprising units having structure I, as described above;
(ii) an oxidation catalyst, as described above, and
(iii) an energy-absorbing compound selected from the group consisting of microwave reactive materials and photoinitiators having a wavelength of maximum absorption of electromagnetic radiation from about 200 nm to about 750 nm; and
(b) exposing the oxygen scavenging composition to electromagnetic radiation for a duration sufficient to initiate oxygen scavenging by the oxygen scavenging composition.
In still another embodiment, the present invention relates to a method of producing an oxygen scavenging polymer, comprising:
(a) polymerizing a monomer composition comprising monomers having structure II: 
wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls, to form an oxygen scavenging polymer.
The present invention provides an oxygen scavenging composition, and packaging articles comprising oxygen scavenging layers comprising the oxygen scavenging composition, which do not generate fragments upon reaction with oxygen. Further, the present invention provides a polymer preparable by direct polymerization, and not reactive extrusion, thus providing an amorphous polymer product with the potential of 100% incorporation of the oxygen scavenging moiety into the polymer and avoiding the problem of polymer degradation frequently found in reactive extrusion processes. The direct polymerization can typically be performed under mild conditions and is easily controlled. Further, the oxygen scavenging polymer of the present invention typically has a high scavenging rate and capacity in the first few days after initiation and package filling.